The invention relates to a borosilicate glass, which is colored bluish, blue to black with Ti.sup.3+ ions, has a low transmission in the near infrared range (NIR) and the composition SiO.sub.2 &gt;78; B.sub.2 O.sub.3 &gt;8; Al.sub.2 O.sub.3 1.5 to 4; alkali oxide&gt;2.
The glasses according to the invention are suitable for decorative applications because of their special absorption transmission characteristic. The applications include, for example, the use as a glass used in home kitchens, filters or, if the light transmissibility in the near infrared range is sufficiently low, the use as an absorber in solar technology.
The coloring of glass with trivalent titanium ions is known. [Ti.sup.III O.sub.6 ] colors the glass, for example, violet or brown. In this connection, reference can be made to the text of H. Scholze entitled "Glas", page 219, Springer Verlag 1988. Absorption bands occur in the range of approximately 400 to 800 nm in dependence upon the glass composition and the melt conditions.
It is also known that Ti.sup.3+ ions, for example, in silicate glasses, can be stabilized only with difficulty. Here, reference can be made to the article of G. H. Sigel entitled "Optical Absorption of Glasses" published in the Treatise on Materials Science and Technology, Volume 12, page 38, Academic Press 1977.
When carbon or compounds containing carbons are used as a reducing agent, then large and nonuniform melting losses can be expected so that the color of the glass can only be reproduced with difficulty.
If metal or metal oxides are used as a reducing agent, these metals are built into the glass as oxides, then specific glass characteristics can change in an unwanted manner, for example, by an increase of the thermal expansion or by additional coloring effects occurring.
Furthermore, it can at times be necessary to adjust the oven atmosphere to increase the intensity of reduction in order to prevent the reoxidation of Ti.sup.3+ ions to non-coloring Ti.sup.4+ ions.
For high melting glasses such as borosilicate glasses, problems can occur in this manner when adjusting the necessary high temperatures.
It is furthermore known to color glass with cobalt compounds. Heavy metals can, however, have toxic effects when the glass is chemically attacked and dissolved components reach, for example, the drinking water. For this reason, the use of cobalt compounds must be excluded. Cobalt colored borosilicate glass furthermore has no or no adequate absorption in the near infrared range.